The present invention relates to a copper or copper alloy target/copper alloy backing plate assembly having characteristics required in a magnetron sputtering target.
In recent years, sputtering is being employed for forming a thin film to be used in semiconductor devices and various electronic components. As well known, this sputtering method is a deposition method of irradiating charged particles toward a target, sputtering particles from the target with the impact strength of such particles, facing the foregoing target and forming a thin film, which is primarily composed of the target material substance, on a substrate such as a wafer.
A target used in this sputtering deposition method is usually formed in a tabular shape or discoid shape, and this target is generally bonded to a backing plate.
Since the target will be subject to a significant impact of the charged particles during sputtering, temperature of the target will rise gradually.
Thus, it is necessary to cool the target, and, with most targets, a material (backing plate) with high thermal conductance such as aluminum alloy, stainless steel or oxygen free copper is bonded to the back face thereof via soldering, diffusion bonding, pressure bonding or bonding using the anchor effect in order to form a target-backing plate assembly.
And, in order to cool this backing plate from the outside via a cooling means, a cooling plate also having high thermal conductance is additionally bonded thereto in order to absorb the heat of the target.
In recent years, sputtering is being conducted with higher power, and copper alloy having high strength, high thermal conductance, and high electrical conduction property is being widely used as the backing plate material. Further, bonding of the target and backing plate is often conducted solidly with the diffusion bonding method or the like.
Conventional technology is briefly described below.
There is an example of engaging and bonding a sputtering target to a beryllium copper alloy backing plate (for instance, refer to Patent Document 1), and an example of diffusion bonding an aluminum alloy target/Cu-1% Cr backing plate (for instance, refer to Patent Document 2).
Further, a copper alloy backing plate having a 0.2% proof stress of 200 MPa or greater; for instance, a copper alloy having Cu-0.7 to 1.2 wt % Cr and in which the total content of components selected from Al, Mg, S, K, Ca, Fe, Ni, As, Ag, Sb and Bi is 1 wt % or less is introduced (for instance, refer to Patent Document 3).
Patent Documents 4 to 6 refer to the eddy current in magnetron sputtering.
In particular, Patent Document 6 describes that the eddy current that occurs due to the rotation of the magnet in magnetron sputtering deteriorate the uniformity of the film, and illustrates the use of aluminum alloy or copper alloy wherein the specific resistance is 3.0μΩ·cm or greater and the strength is 150 MPa or greater.
Among the above, the Examples describe industrial aluminum alloy of 4.9μΩ·cm and 182 MPa, and brass of 7.2μΩ·cm (24% IACS) and 320 MPa; and the Comparative Examples describe Al-0.5Cu of 75 MPa, and a Cu—Cr backing plate of 2.1μΩ·cm (82% IACS) and 465 MPa.
Further, Patent Document 7 proposes a backing plate material capable of preventing thermocompression bonding with the target with Cu having a purity of 99.7% and adding a subelement of 100 to 3000 wtppm (0.01 to 0.3 wt %). The added element in this case is of an extremely minute amount, and a backing plate material placing emphasis on thermal conductance is being proposed.
[Patent Document 1] U.S. Pat. No. 5,269,899
[Patent Document 2] Japanese Patent Laid-Open Publication No. H10-330929
[Patent Document 3] Japanese Patent Laid-Open Publication No. H11-236665
[Patent Document 4] Japanese Patent Laid-Open Publication No. H3-134170
[Patent Document 5] Japanese Patent Laid-Open Publication No. H10-195649
[Patent Document 6] Japanese Patent Laid-Open Publication No. 2001-329362
[Patent Document 7] Japanese Patent Laid-Open Publication No. H1-180975
Nevertheless, the foregoing conventional backing plates have the following problems.
As a specific example, there is minute copper wiring (for instance the 90, 65 nm wiring rule) formed with the Damascene Process. With this process, after forming a barrier film of tantalum or tantalum nitride in the wiring groove, a copper or copper alloy film is sputtered as a seed layer. Nevertheless, in order to form this kind of thin seed layer, it is necessary to improve the ionization ratio of the sputtered particles via high-power sputtering so as to control the deposition.
For example, with the brass backing plate described in the Examples of Patent Document 6, sufficient uniformity of the film cannot be obtained. Further, with the Cu—Cr backing plate described in the Comparative Examples, there is a problem in that sufficient uniformity cannot be obtained due to the magnet rotation involving the eddy current.
Every backing plate described in the foregoing Patent Documents is not suitable and has problems. Detailed explanation will be provided based on the Examples and Comparative Examples described later.